Cylindrical roller bearings are widely used in various types of rotating machines. As a cylindrical roller is an important component of the cylindrical roller bearing, excircle surfaces machining precision of the cylindrical roller directly impacts the performance of the cylindrical roller bearings. Main methods of precision machining on excircle surfaces of cylindrical components include super-finishing methods and double-disc planetary grinding methods.
The super-finishing method is a micro finishing method, which can achieve micro cutting effects, by using a fine-grained whetstone as a grinding tool, such that the whetstone may apply load on a workpiece and perform a low-speed axial movement as well as a micro-reciprocating vibration relative to the workpiece. At present, a mostly used method of precision machining on excircle surfaces of the cylindrical roller is a through-feed centerless super-finishing method, which involves devices consisting of two guide rollers and a super-fine head assembled with a whetstone, the guide roller supporting and driving the workpiece to perform a low-speed spiral movement, the super-fine head applying a comparative low pressure to press the whetstone to the workpiece, the whetstone achieving a surface contact with the workpiece, and at the same time the whetstone performing a high-frequency vibration along an axial direction. During the process of the through-feed centerless super-finishing method, cylindrical rollers of successively penetrate processing areas and subject to be superfinished by the whetstone, and until all the cylindrical rollers have passed through the processing area for several times, a certain super-finishing process (rough finishing process, Fine finishing process, or super finishing process) ends. The through-feed centerless super-finishing method can improve the surface roughness of the workpiece (the through-feed centerless super-finishing method usually may obtain an accuracy up to Ra 0.025 μm), remove a surface degenerating layer formed by a prior process, and improve a roundness of the workpiece. Except for wear conditions of the whetstone and the super finishing roller, as well as differences of the cylindrical roller itself, each cylindrical roller share common super finishing conditions and parameters.
However, due to the limitations of processing principles, the super-finishing method involves following technical defects. In one aspect, variations of wear conditions of the whetstone and the super finishing roller are unfavorable for improving cylindrical surface size accuracy and shape accuracy of the cylindrical roller; in the other aspect, as in the through-feed centerless super-finishing method, only a limited number of cylindrical rollers are processed at the same time, and material removal amounts therein are almost independent of the difference between diameter thereof with that of the other cylindrical rollers of the same batch, so the through-feed centerless super-finishing method cannot obviously reduce the diameter difference of the cylindrical rollers. The above two aspects may lead to a slow improvement on excircle surface finishing precisions (shape accuracy and dimensional consistency) of the workpiece, a long processing cycle, and a high cost.
The main structure of a double-disc planetary cylindrical-component grinding device includes an upper grinding disc, a lower grinding disc, a planetary wheel retainer, an outer ring gear and an inner ring gear. The upper grinding disc and the lower grinding disc are coaxially arranged and respectively rotate independently, the upper plate grinding disc functioning to apply pressure. The planetary wheel retainer is placed between the inner ring gear and the outer ring gear, and a cylindrical roller is placed in a hole of the retainer, with the hole radically distributed on a surface of the retainer. During a grinding process, the retainer performs a revolution around a center of the grinding disc as well as a self rotation, under the effect of the upper and lower discs as well as the retainer, while the cylindrical roller performs a revolution around a center of the retainer and at the same time a rotation around an axis itself, thus involving a complicated spatial motion. A micro material removal is achieved under an effect of grinding solutions between the upper and lower grinding discs. Double-disc planetary cylindrical components grinding device can achieve an excircle surface of cylindrical workpiece with a high precision, for example, for a workpiece with a length of 30˜40 mm, after a super-finishing of a double-disc grinding machine, a roundness error of less than 0.001 mm may be achieved, a vertical section diameter consistency may be less than 0.002 mm, and a surface roughness is less than Ra 0.025 μm. However, the double-disc grinding machine can only be used for excircle super-finishing on small batch (dozens to hundreds) of cylindrical workpiece. For the large volume of bearing roller demand, it is difficult for the double-disc planetary grinding method to meet.
It can be seen that there is an inherent lack of processing precision when the excircle surface of the cylindrical workpiece is processed by the through-feed centerless super-finishing method, while the double-disc grinding method cannot meet the demand of a mass production, and thus there is an urgent need for a super-finishing device for excircle surface of the cylindrical component, which may achieve a high processing precision and a mass production, so as to meet requirements of the high precision cylindrical roller bearing on the processing precision of excircle surfaces of the cylindrical rollers, as well as the demand of production scales.